1. Field of the Invention
The present invention relates to a method of detecting a circular routing in No. 7 signaling network, more specifically, a method of detecting a circular routing in No. 7 signaling network to prevent a congestion of links by the circular routing and finding out any reasons of the link congestion by detecting the circular routing occurred when operating the signaling network.
2. Description of the Related Art
Differing from an existing communication path system using a communication path and a signal path together, generally, No. 7 signaling system is a common signaling system, in which a number of voice signals transmit and receive a signal information through each independent single channel by completely separating the communication path and the signal path.
A common constitution of No. 7 signaling network to which No. 7 signaling system as mentioned above is applied includes signaling points (SP) and signaling links (SL) as illustrated in FIG. 1.
In view of constitution, a signaling point of sending, receiving or transmitting a signal message generated by a user sends, receives or transmits the signal message to another signaling point, which includes a signaling end point (SEP) to send or receive the signal message at the signaling point and a pair of signaling transfer points (STP) to transmit a message from one signal link to another signal link. The signaling end point (SEP) consists of an origination point (OP) to generate the signal message and a destination point (DP) being a destination of the signal message.
As shown in FIG. 1, a No. 7 signaling network includes any of signal end points SEP1 (11) and SEP2 (12); direct locals STP1 (21) and STP2 (22) being directly connected to SEP1 (11); and remote sites STP3 (23) and STP4 (24) being connected to SEP1 (11) through locals STP1 (21) or STP2 (22). The No. 7 signaling network includes A-links 1, 2 (1, 2) directly connecting locals STP1 (21) and STP2 (22) with SEP1 (11); E-links 1, 2 (3, 4) connecting remote sites STP 3 (23) and STP4 (24) with SEP1 (11); C-links 1, 2 (5, 10) connecting local STP1 (21) with local STP2 (22) or local STP1 (23) with local STP2 (24); and B-links 1, 2, 3, 4 (6, 7, 8, 9) connecting each of local STP1 (21) and STP2 (22) to each of STP3 (23) and STP4 (24) or each of STP4 (24) and STP3 (23).
In general, the E-links 1, 2 (3, 4) are connected with the No. 7 signaling network is connected and used, while the E-links 1, 2 (3, 4) are connected. When A-link  1 (1) is in an unavailable state, the signaling network is connected to SEP1 (11) using A-link 2 (2); and when even A-link (2) is in an unavailable state, the signaling network stops.
When E-links 1, 2 (3, 4) are connected used, even though A-links 1, 2 (1, 2) are all interrupted, No. 7 signaling network can be connected to SEP1 (11), using E-links 1, 2 (3, 4).
However, if A-links 1, 2 (1, 2) and E-links 1, 2 (3, 4) at SEP1 (11) become all inactive state while No. 7 signaling network is operated by using E-links 1, 2 (3, 4), a circular routing occurs such that the message sent from SEP2 (12) to SEP1 (11) circulates among the signaling transfer points (STP).
For example, when sending a message at SEP2 (12) to SEP1 (11), if A-link 1 (1) between SEP1 (11) and local STP1 (21) becomes an inactive state, the message concentrates into A-link 2 (2), and thus A-link 2 (2) becomes the inactive state. In sequence, E-links 1, 2 (3, 4) become the inactive state due to a congestion of messages by the same reason.
When the A-links 1, 2 (1, 2) and E-links 1, 2 (3, 4) are all inactive state, the signals transmitted from SEP2 (12) continue circulating among STP1 (21), STP2 (22), STP3 (23) and STP4 (24).
As depicted above, in the event that the circular routing occurs in No. 7 signaling network, the traffic among STPs continuously increases and a congestion of links is caused. Furthermore, there may be a problem making it is impossible to find out any reasons of the link congestion.
Therefore, it is necessary to detect the circular routing in advance to prevent a congestion of links. In this connection, the circular routing occurred between two STPs is automatically detected in the system, thereby preventing the congestion of links.
Further, the circular routing occurred among three or more nodes such as among three or more STPs is detected by using a message transfer part routing verification test (MRVT) of an operation and maintenance application (OMAP) as shown in FIG. 1.
FIG. 2 is a flow chart to depict a method of detecting a circular routing in No. 7 signaling network according to the related art.
For a circular routing detection, after a command to detect the circular routing is input by an operator (S10), in FIG. 2, signal routes being capable of transmitting signals to a specific destination point code (DPC) are detected (S12).
Then, in step S12, the MRVT message is transmitted to all signal routes as detected (S14); the DPT waits until a response message to the MRVT message is received.
Upon receiving the response message to the MRVT message (S16); whether or not the received message is a MTP routing verification acknowledgement (MRVA) is checked (S18). If it is the MRVA message, the corresponding signal route is determined as a normal state(S20). However, if a MTP routing verification result (MRVR) message rather than the MRVA message is received, it is determined that a circular routing occurs in the corresponding signal route and this state is informed to the operator (S22).
At the other STP received the MRVT message transmitted at step S14 (S30), the received response message determines whether a self station is the destination point code (DPC) of the MRVT message (S32). If the station is the DPC, the MRVA message is transmitted to the other STP to transmit MRVT as the message is correctly received as the normal state(S35), and if the station is not the DPC of the MRVT message, all signal routes being capable of transmitting signals to the corresponding DPC are detected (S36).
Among the signal routes detected in step S36, there may be the routes in which the circular routing has already occurred. While the MRVT message is transmitted, all STP information is stored. Therefore, the routes with the circular routing as occurred are determined from the signal routes detected at S36, based on a history of the stored MRVT (S38), and the circular routing as occurred is informed to the other STP which transmits MRVT as the MRVR message (S40).
Through the signal routes which fail to determine the circular routing as occurred at step S38, the MRVT message is re-transmitted (S42). Then, if the response message is received (S44), and the response message is delivered to STP which transmits the MRVT message (S46).
To specify in reference to FIG. 1, when transmitting signals having SEP1 (11) as a destination point, if the A-links 1, 2 (1, 2) and E-links 1, 2 (3, 4) are all in an unavailable state, an operator checks out whether or not a circular routing occurs. Herein, when the operator input the command to detect the circular routing as occurred at STP2 (22), STP2 (22) detects the signal routes having SEP1 (11) as the DPC and being capable of transmitting the signals.
As illustrated in FIG. 1, the signal routes to transmit signals from STP2 (22) to SEP1 (11) are A-link 2 (2), C-link 1(5), B-link 2 (7) and B-link 4(9). As the A-link 2 (2) is in an unavailable state, the signals can be and B-link 4 (9).
Therefore, STP2 (22) transmits the MRVT message having SEP1 (11) as DPC to the above-mentioned C-link 1 (5), B-link 2 (7), B-link 4 (9).
To select one signal route and explain it, the MRVT message transmitted to C-link 1 (5) is delivered to STP1 (21), which checks whether or not the station is DPC of MRVT.
Since the DPC of MRVT is not STP1 (21), STP1 (21) checks the signal routes to be re-usable and to transmit the MRVT to the B-link 1(16), B-link 3 (8) and C-link 1 (5).
As MRVT has already passed through the C-link 1 (5), the history information of C-link 1 (5) is stored. Thus, the STP1 (21) determines that the circular routing is occurred in C-link 1 (5) and transmits the MRVR message to STP2 (22).
In addition, upon transmitting the MRVT message and receiving a response message, the other B-links 1, 3 (6, 8) again transmit the response message to STP2 (22).
In the same way, a related art detects the circular routing by using the MRVT message of the Operation and Maintenance Application (OMAP). In the related art, all signal routes are tested in connection with DPC of the MRVT message. Therefore, the related art has a few problems to cause any unnecessary load to the whole signaling network, to make a required time for test longer and to make it impossible to prevent a congestion of links.
Furthermore, if A-link or E-link is in an unavailable state and so the circular routing detection is performed using the MRVT message, this only increases load in No. 7 signaling network. As the circular routing detection is performed by the operator's command/instruction, there is also the problem that it is impossible to perform the circular routing detection at an appropriate time when A-link or E-link is in an unavailable state.